In a so-called laser ignition, a laser beam is focused into the combustion chamber of an internal combustion engine and ignites the fuel-air mixture present in the combustion chamber in this manner. This requires a so-called laser device, in which the laser beam is generated and focused. In order to decouple the interior of the laser device from the combustion chamber in whose interior high pressures and temperatures naturally prevail, what is known as a combustion-chamber window is provided on the laser device. As the name already implies, this combustion-chamber window is transmissive for the laser beam and may also have a focusing effect. To ensure a fault-free operation of the laser ignition, the combustion-chamber window should be penetrable for the laser radiation across the entire service life of the internal combustion engine. However, it may happen that the necessary optical transparency of the combustion-chamber window is lost due to deposits of exhaust gas on the combustion-chamber window.
In order to prevent these deposits, the laser device should be designed in such a way that the operating temperature on the surface of the combustion-chamber window facing the combustion chamber is high enough to burn off or oxidize deposits, especially organic deposits.
However, the surface temperature of the combustion-chamber window must not reach a level at which self-ignitions of the fuel-air mixture at the surface of the combustion-chamber window occur.